Knowing your dissolved oxygen levels won’t help unless you have an internal standard, a dedication to monitoring, and a plan for fixing your problems. In my many years of working with brewers, I’ve found that those who set a goal and commit to that metric do the best. So the first step in your monitoring program should always be a comprehensive picture of the amount of dO2 you are willing to tolerate at each step of the process, not just the finished product.
Let’s say the dO2 in your bright beer tank (BBT) exceeds your standard. How do you trace it back to the root cause, and then how do you mitigate the issue with that particular tank? The first step is to check the dO2 in your fermentation or aging tank. If it’s just a few ppb, take your portable meter and move to a sample point just before the BBT. If your dO2 still looks great, then it’s a good bet that air in the BBT before filling is causing your high readings.
But what if you saw a high reading in the sample right before the BBT? In that case, go back to the fermentation vessel and start looking again, moving to the next sample point. Keep moving toward the BBT. As soon as you find significantly higher readings, leave the analyzer in place and systematically move backward through the process to make sure that all valves, fittings, and pipe connections are tight. Then look at levels before and after pumps, filters, and centrifuges — any fitting that could possibly contribute. It may be as simple as a valve that’s open on the suction side of a pump.
Now, let’s say you’ve looked at all the possible culprits and your high dO2 is happening after a pump or centrifuge. What do you do? Some pumps and centrifuges can seem fine when they start, but as they heat up from use, they pull more oxygen into the beer. By checking the dO2 levels at different times throughout your filtration process, you can really zero in on whether or not heat and excess load are causing problems.
I have a customer who occasionally monitors their whole filtration run by placing a portable dO2 analyzer with on-board data logging on the filter outlet, collecting data throughout the entire filtration process. By doing this every so often, they’ve been able to determine when it’s time to rebuild pump seals. His pump load was increasing toward the end of the run due to the increased pressure it took to push the beer through the filter, so his O2 levels would start to climb drastically.
My final thought brings us back to my blog post from last Thursday. Measuring during or just after any movement of beer will help you recognize whether there is a significant infusion of oxygen into your product. If things looked good at the beginning of a run, but not so great at the end, you can probably pinpoint the problem by monitoring throughout the run the next time you move your beer.